LONDON — The top U.S. commander in Iraq briefed the United States’ closest ally on the course of the war Tuesday, praising Britain’s plan to give Iraqi security forces control in Basra but warning against leaving the country too soon.

The visit to Britain by Gen. David Petraeus and U.S. Ambassador Ryan Crocker comes a week after their testimony to American lawmakers, which cited recent gains in security and a decrease in sectarian killings but warned of little political progress in Baghdad.

“There are no easy answers or quick solutions to helping the Iraqis build sustainable security and achieve national reconciliation,” Petraeus said. “Our assessments underscore the importance of recognizing that a premature drawdown of our forces would likely have devastating consequences not only for Iraq and the region, but for our nations and the world.”

Speaking before a meeting with Prime Minister Gordon Brown, Petraeus constantly praised British forces serving in Iraq, repeating his assessment of stability in Iraq in the wake of the “surge” of American forces.

He also offered support for Britain’s plan to give Iraqi security forces control of Basra province later this year or earlier next year.

“In the four southern provinces of Iraq, under the British-led multinational division, the transition to overwatch is already well along,” he said.

“While there have been challenges and setbacks ... Iraqis have generally been able to deal with the challenges with minimal assistance, although help has been provided on occasion.”

Britain is reducing Iraq forcesBrown will outline his plans for British troops in a speech to Parliament next month. British defense minister Des Browne has said there may be some reduction in numbers when soldiers ending current tours are replaced in November and December.

President Bush has embraced Petraeus’ plan to withdraw 5,700 troops from Iraq by the end of the year and reduce the force from 20 combat brigades to 15 brigades by next July. Petraeus is expected to make a further assessment and recommendations in March.

There are about 169,000 U.S. troops in Iraq.

Britain is reducing its force in Iraq to 5,000, mostly based around Basra, Iraq’s second-largest city, 340 miles southeast of Baghdad.

Calm has largely prevailed in the predominantly Shiite city of about 2 million since the British soldiers pulled back to the airport, handing over responsibility to Iraqi security forces.

Former British Prime Minister Tony Blair paved the way for the move in February, when he ordered a troop reduction from 7,100 to 5,500.

Details of meetingBrown’s Downing Street office said Petraeus and Brown discussed security in Basra and the U.S. commander’s assessment of progress in Iraq during an hour of talks.

Brown “reiterated that like America, Britain will discharge its duties to the Iraqi people, to our allies and to the international community,” a spokesman said, speaking on condition of anonymity in line with government policy.

“They agreed it was essential for Iraq to achieve a more stable and confident political process,” the spokesman said. Both men hope to see “reconciliation with disaffected groups, economic development in Iraq, a more inclusive government, and a genuine attempt to reach consensus on major political issues.”